Plagued by pollution, Tokyo in the year 2040 has become a grimy shadow of itself. That's why an organization known as DC is conducting research and trying to clean up Tokyo with advanced robots called RTs. Young, hotheaded Ken Ando wants to get into DC, but he initially fails the training course, so when a mysterious giant robot drops out of the sky during a routine mission, Ken--determined to prove himself--takes over another squad member's RT and fends off the invader. Ken gets a second chance and is admitted to DC, but the existence of the giant robot and its repeated visits are changing things for the organization. They activate Balcion, a battle robot, and start fitting the RTs with weapons too. Things get worse when, during one of the giant robot's invasions, it disappears in a black explosion and takes another RT pilot, Mizuki, with it. Mizuki returns a few days later claiming that the giant robot is named Cybuster, a sentinel from an alternate world called La Guias. But with a story so outrageous, will anyone believe Mizuki--even Ken, who's known her since childhood? (Synopsis courtesy of animenewsnetwork.com)